Screening of adjuvants for bioherbicide formulations with Colletotrichum spp. and Phoma spp.

A study was conducted to determine whether certain surfactants (Tween series: 20, 40, 80, and Tergitol NP series: 9, 10) and adjuvants (sorbitol and gelatin) would be useful components in bioherbicide formulations of Colletotrichum (10 isolates) and Phoma (5 islolates). The effect of adjuvants on conidial germination and mycelial growth varied with adjuvant, adjuvant concentration (0.01, 0.1, 1, and 5%), fungal isloates, and conidial density (105–108 conidia/ml). Tween 20 reduced germination and mycelial growth in some Phoma and all Colletotrichum isolates, whereas Tween 40 and Tween 80 stimulated germination without detrimental effects on mycelial growth of all isolates. Tween 40 and Tween 80 released conidia from self-inhibition of germination in Colletotrichum as compared to the germination of conidia at 107 conidia/ml in the absence of the adjuvant. Tergitol NP often reduced germination and mycelial growth. There were no trends in fungal responses to sorbitol. The responses of Colletotrichum were highly variable to gelatin, but for Phoma, gelatin increased germination and mycelial growth, and also released self-inhibition of germination. In summary, gelatin, Tween 40, and Tween 80 were useful components for bioherbicide formulations to increase conidial germination and mycelial growth of Phoma, whereas Tween 40 and Tween 80 were useful for Colletotrichum.